String.prototype.localeCompare()
The localeCompare()
method returns a number indicating
whether a reference string comes before, or after, or is the same as the given string in
sort order.
The new locales
and options
arguments
let applications specify the language whose sort order should be used and customize the
behavior of the function. In older implementations, which ignore the
locales
and options
arguments, the
locale and sort order used are entirely implementation-dependent.
Syntax
localeCompare(compareString)
localeCompare(compareString, locales)
localeCompare(compareString, locales, options)
Parameters
compareString
-
The string against which the
referenceStr
is compared. locales
andoptions
-
These arguments customize the behavior of the function and let applications specify the language whose formatting conventions should be used. In implementations which ignore the
locales
andoptions
arguments, the locale used and the form of the string returned are entirely implementation-dependent.See the
Intl.Collator()
constructor for details on these parameters and how to use them.
Return value
A negative number if referenceStr
occurs
before compareString
; positive if the
referenceStr
occurs after compareString
;
0
if they are equivalent.
Description
Returns an integer indicating whether the referenceStr
comes
before, after or is equivalent to the compareString
.
-
Negative when the
referenceStr
occurs beforecompareString
-
Positive when the
referenceStr
occurs aftercompareString
- Returns
0
if they are equivalent
Warning: Do not rely on exact return values of -1
or 1
!
Negative and positive integer results vary between browsers (as well as between
browser versions) because the W3C specification only mandates negative and positive
values. Some browsers may return -2
or 2
, or even some other
negative or positive value.
Performance
When comparing large numbers of strings, such as in sorting large arrays, it is better
to create an Intl.Collator
object and use the
function provided by its compare
property.
Examples
Using localeCompare()
// The letter "a" is before "c" yielding a negative value
'a'.localeCompare('c'); // -2 or -1 (or some other negative value)
// Alphabetically the word "check" comes after "against" yielding a positive value
'check'.localeCompare('against'); // 2 or 1 (or some other positive value)
// "a" and "a" are equivalent yielding a neutral value of zero
'a'.localeCompare('a'); // 0
Sort an array
localeCompare()
enables case-insensitive sorting for an array.
let items = ['réservé', 'Premier', 'Cliché', 'communiqué', 'café', 'Adieu'];
items.sort( (a, b) => a.localeCompare(b, 'fr', { ignorePunctuation: true }));
// ['Adieu', 'café', 'Cliché', 'communiqué', 'Premier', 'réservé']
Check browser support for extended arguments
The locales
and options
arguments are
not supported in all browsers yet.
To check whether an implementation supports them, use the "i"
argument (a
requirement that illegal language tags are rejected) and look for a
RangeError
exception:
function localeCompareSupportsLocales() {
try {
'foo'.localeCompare('bar', 'i');
} catch (e) {
return e.name === 'RangeError';
}
return false;
}
Using locales
The results provided by localeCompare()
vary between languages. In order
to get the sort order of the language used in the user interface of your application,
make sure to specify that language (and possibly some fallback languages) using the
locales
argument:
console.log('ä'.localeCompare('z', 'de')); // a negative value: in German, ä sorts before z
console.log('ä'.localeCompare('z', 'sv')); // a positive value: in Swedish, ä sorts after z
Using options
The results provided by localeCompare()
can be customized using the
options
argument:
// in German, ä has a as the base letter
console.log('ä'.localeCompare('a', 'de', { sensitivity: 'base' })); // 0
// in Swedish, ä and a are separate base letters
console.log('ä'.localeCompare('a', 'sv', { sensitivity: 'base' })); // a positive value
Numeric sorting
// by default, "2" > "10"
console.log("2".localeCompare("10")); // 1
// numeric using options:
console.log("2".localeCompare("10", undefined, { numeric: true })); // -1
// numeric using locales tag:
console.log("2".localeCompare("10", "en-u-kn-true")); // -1
Specifications
Specification |
---|
ECMAScript Language Specification # sec-string.prototype.localecompare |
ECMAScript Internationalization API Specification # sup-String.prototype.localeCompare |
Browser compatibility
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